In developing higher efficiency catalysts for NOx abatement from stationary emission sources utilizing selective catalytic reduction (SCR), comparison test conditions, including gas composition and gas flow rates, are needed that approximate industrial operating conditions. Standard tests will be fuel-dependent, i.e. typical flue gas from a coal-fired electrical utility plant might consist of 150-1000 ppm NO, 5% O-2, 13% CO2, 8% H2O, and 200-2000 ppm SO2, while that from a plant utilizing natural gas would contain appreciably more O-2, less NO, and very low SO2. For low temperature catalysts developed for placement after the electrostatic precipitator (ESP) and desulfurization units, flue gas would essentially be dust- and sulfur-free. Protocols are given for comparison testing of NOx abatement catalysts using ammonia as the reductant. These test conditions are used in the comparison of Cu-, Fe-, and V-containing ZSM-5 and mordenite catalysts. It was found that initial NO conversion levels were lower than those achieved after a thermal pretreatment of the catalysts. Under the reaction conditions employed, moisture was an inhibitor for the Fe- and V-containing catalysts but was a promoter for the Cu-mordenite catalyst. The V-ZSM-5 catalyst exhibited a stable activity for NO reduction in the presence of H2O and SO2 but rapid deactivation was observed in the presence of 10 ppm SO3. (C)2000 Elsevier Science B.V. All rights reserved.